The invention relates generally to marine engines, and more particularly, to controlling exhaust venting.
Outboard engines include a drive shaft which extends from the engine power head, through an exhaust case, and into an engine lower unit. The lower unit includes a gear case, and a propeller shaft extends through the gear case. Forward and reverse gears couple the propeller shaft to the drive shaft. The drive shaft, gears, and propeller shaft sometimes are referred to as a drive train.
An exhaust path extends from the power head through the exhaust case. The gear case includes an exhaust passageway, and at least some types of propellers include an outer hub through which exhaust gases are discharged. In operation, exhaust from the power head flows through the exhaust case, the gear case passageway, and the propeller.
To increase acceleration of the engine from an idle condition, it is known to provide vent openings in the propeller or gear case so that some exhaust is discharged through the vent openings and into a region adjacent blades of the propeller. By displacing at least some of the water adjacent the propeller blades, the propeller is more easily accelerated. That is, the propeller blades more easily move through an exhaust-water combination rather than only water.
Known vent openings have fixed dimensions and are not readily adjustable. For example, vent openings in a propeller typically are drilled or machined in the propeller. Such openings have fixed dimensions, e.g., a fixed diameter. Plugs may be utilized to completely close the vent openings. An operator therefore can select whether to operate with the plugs in place, i.e., no venting of exhaust gases, or without the plugs, i.e., full venting of the exhaust gases.
It also is known to provide an assortment of plugs for propeller vent openings that have pre-defined fixed dimensioned openings therethrough. The propeller plugs are interchangeable so that an operator can select an amount of venting by selecting a plug having an opening size corresponding to the desired amount of venting.
Propeller vent openings are typically located adjacent each blade. For a four blade propeller, for example, four vent openings are located in the propeller with each vent opening being adjacent one blade. In addition, for consistent performance, the size of the vent openings should be the same at each propeller blade. Otherwise, the blades will be subjected to different operating conditions which can result in variable, and degraded, performance of the propeller.
With the interchangeable, fixed dimension propeller vent plugs described above, an operator may possibly purchase and test multiple sets of vent plugs. For example, an operator may purchase three or more sets of four vent plugs for a four blade propeller, and test each set of plugs to determine which set provides the desired performance. Once the plugs are tested by the operator and one set of plugs is selected, the other plugs which the operator determines not to use probably are not returnable since the plugs will have been used and may show some wear. In addition, retailers would have to stock many different vent plugs having different sized vent openings.
A vent plug that includes a user adjustable, variable sized vent opening is described herein. Rather than being removable and replaced with a plug with a different sized opening, the present vent plug is fixed in place and is not ordinarily removed except in circumstances of repair. A user need not remove the vent plug in order to adjust the size of the vent opening.
More specifically, and in an exemplary embodiment, the vent plug includes a main body configured to be snap-fit and secured within an opening in a wall of a gear case in flow communication with an exhaust passageway through the gear case. The vent plug main body also can be configured to be snap-fit and secured within an opening in a propeller hub and in flow communication with an exhaust passageway through the propeller.
The vent plug main body also includes a flow passage therethrough. The flow passage extends from an inlet side of the main body to an outlet side of the main body. A planar flow restriction member extends across the flow passage, and an opening extends through the flow restriction member. The size of the opening in the flow restriction member limits the maximum amount of exhaust which can be discharged through the vent plug.
The main body also includes a variable flow restriction member chamber. In the exemplary embodiment, the chamber has a generally circular cross sectional shape. An annular groove in the main body member extends around the chamber.
A variable flow restriction member is located in the chamber, and in one embodiment, the member is a disk having an annular ridge at its periphery. An opening extends through the disk, and the disk opening has the same diameter as the diameter of the opening in the flow restriction member. The disk is movable within the chamber with the disk ridge moving within the chamber groove.
When the disk opening is coaxially aligned with the flow restriction member opening, the plug is in a fully open position so that maximum exhaust flows through the plug. When the disk opening is not overlapping the flow restriction member opening, then the plug is in a fully closed position. When the disk opening partially overlaps the flow restriction member opening, then the plug is in a partially open position so that at least some exhaust flows through the plug. The disk is adjustable to various positions between the fully closed and the fully open position to enable an operator to select an exhaust flow which results in the desired performance.
The above described vent plug including the user adjustable, variable sized vent opening enables a user to select a specific amount of exhaust flow for a particular engine without requiring the purchase and test of multiple sets of vent plugs. In addition, retailers do not have to stock many different vent plugs having different sized vent openings. Rather, retailers can stock only the above described vent plug.